Upgrade django and python versions

[brunomichetti]

Changes:

• Minor fix in _make_token_with_timestamp function, adding missing parameter to support newer version of django
• Add in CONTRIBUTING.md file a step by step guide to run pytest locally
• Split github actions tests into two files: one for test and one for coverage
• Fix tests and coverages in github actions
• Install tox to run locally the tests with different versions of Python
• Remove support for older versions of Python before 3.8
• Remove support for older versions of Django before 4.2
• Update README to have the version badges
• Update install_requires in setup.py for the working versions

TODO:

• Install dev tools (isort, black, flake8, mypy) and add them into the github actions